The keyboard has been an indispensable device in the current computer system, and keyboard design is also diversified to meet various application occasions of computer systems. For a dim or dark environment, manufacturers had developed several self-luminous keyboards to enable users to accurately press correct keys. For example, U.S. Pat. No. 5,936,554 and No. 7,278,750, Taiwan patents No. 566612 and No. 581961 respectively disclosed keyboard devices having LED inside keys, wherein each single key is illuminated by the LED thereinside, whereby users can make out the keys in a dim or dark environment. The prior arts can indeed solve the abovementioned problem. However, a standard keyboard may have over one hundred keys, and the prior-art keyboard devices need the same number of LEDs, which not only increases the fabrication steps and cost but also impairs the lightweighting of keyboards. Besides, numerous LEDs consume a lot of power and generate considerable heat.
For other types of self-luminous keyboards, refer to U.S. Pat. Nos. 6,179,432, 6,199,996, 6,217,183, 6,284,988, 6,322,229, 6,554,442, 6,590,508, 6,648,530, 6,860,612, 7,235,752, 7,239,303 and 7,388,167, and Taiwan patents Nos. 509955, 516671, 587800, 594546, I230957, I231693, M240668, and M313281, wherein a backlight plate, such as an electroluminescent sheet or an optical fiber panel, is arranged over or below a baseplate of a keyboard, whereby light permeates between the keys enable users to make out the keys. In such a type of self-luminous keyboards, the entire keyboard is lightened by a single backlight plate, which can reduce the number of components and simplify the assemblage. Besides, the electroluminescent sheet and the optical fiber panel consume very little power and favor the long time usage of a self-luminous keyboard. However, this type of self-luminous keyboards needs a backlight plate arranged above or below the baseplate, which increases the thickness and impairs fabricating a slim keyboard.